The invention relates to the solvent refined coal process and the use of an improved filteraid material for removing undissolved solids from the liquefied coal slurry resulting therefrom.
One process for the solvent refining of coal generally comprises reaction of a coal/solvent mixture with a reducing gas at high temperature and pressure. After reaction, the resulting liquefied coal slurry is treated to remove a substantial portion of undissolved solids contained therein. These undissolved solids, which include mineral matter, carbonaceous residue and other insoluble material, frequently have a particle size in the micron and submicron range.
One means currently employed for removing these undissolved solids from the liquefied coal slurry is a pressure filtration system. Such systems, which may be of the batch, cyclic or continuous filtration types known in the art, include a support means, such as a screen or the like, for receiving a coating of filteraid material thereon capable of retaining the solids from the coal slurry. One method of utilizing a pressure filtration system is the "pre-coat" procedure, wherein an appropriate amount of filteraid material is deposited on the support prior to passing the coal slurry to be filtered therethrough. This is conventionally accomplished by mixing the material with previously filtered coal liquid or other suitable liquid hydrocarbons and passing the mixture through the support. A second method for utilizing a pressure filtration system is the "body feed" procedure, wherein an appropriate amount of filteraid material is added to the coal slurry to be filtered prior to passing the slurry through the support, whereby the filteraid material and other suspended matter in the slurry are allowed to "build up" on the support to produce a filter cake. The presence of the filteraid in the cake renders it more permeable while retaining dispersed solids. A combination of these procedures may also be employed.